1. Field of the Invention
Exemplary aspects of the present invention generally relate to a cleaning device that removes toner from an image carrier using a cleaning member and an image forming apparatus including the cleaning device.
2. Description of the Background
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile functions, typically form a toner image on a transfer member (e.g., a sheet of paper, etc.) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of a photoconductor; an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet of transfer members; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus.
There is known an electrostatic cleaning device that electrostatically removes residual normally-charged toner (e.g., negatively-charged toner) and reversely-charged toner (e.g., positively-charged toner) from an endless intermediate transfer belt serving as an image carrier. The electrostatic cleaning device includes a first cleaning unit that electrostatically removes the negatively-charged toner and a second cleaning unit that electrostatically removes the positively-charged toner. The first cleaning unit includes a first cleaning brush roller serving as a first cleaning member, to which a positive voltage is applied, and a first collection roller serving as a first collection member that collects the negatively-charged toner attached to the first cleaning brush roller. The second cleaning unit includes a second cleaning brush roller serving as a second cleaning member, to which a negative voltage is applied, and a second collection roller serving as a second collection member that collects the positively-charged toner attached to the second cleaning brush roller.
Each of the first and second cleaning brush rollers contacts the intermediate transfer belt at a position downstream from a secondary transfer position in a direction of rotation of the intermediate transfer belt and opposite a conductive opposing roller around which the intermediate transfer belt is wound. The opposing roller is electrically grounded, and an electric potential difference used for electrostatically cleaning the toner is formed between the intermediate transfer belt and each of the first and second cleaning brush rollers by the voltage applied to each of the first and second cleaning brush rollers. Toner charged to the normal polarity, that is, the negatively-charged toner, is electrostatically removed from the intermediate transfer belt by the first cleaning brush roller. Toner charged to the polarity opposite the normal polarity, that is, the positively-charged toner, is electrostatically removed from the intermediate transfer belt by the second cleaning brush roller.
In another approach, a cleaning device including a polarity control member that gives the toner on the intermediate transfer belt the normal polarity and a normally-charged toner cleaning brush roller that electrostatically removes the normally-charged toner from the intermediate transfer belt has been proposed. The polarity control member is provided upstream from the cleaning brush roller and is supplied with a voltage having the same polarity as the normal charging polarity of toner, that is, the negative polarity. A voltage having the polarity opposite the normal charging polarity of toner, that is, the positive polarity, is applied to the cleaning brush roller.
Each of the negatively-charged toner and the positively-charged toner on the intermediate transfer belt is given a negative polarity when passing through the polarity control member. Accordingly, the toner thus negatively-charged by the polarity control member is electrostatically removed from the intermediate transfer belt by the cleaning brush roller.
However, an untransferred toner image having a larger amount of toner, such as a toner pattern attached to the intermediate transfer belt, cannot be sufficiently removed from the intermediate transfer belt by the above-described related-art cleaning devices.
To solve the above-described problem, the applicant of the present invention has proposed an improved cleaning device that, in addition to the above-described components of the related art, further includes a pre-cleaning unit provided upstream from, for example, the first and second cleaning units in the first example of the related-art cleaning device, and from the polarity control member in the second example of the related-art cleaning device. The pre-cleaning unit includes a pre-cleaning brush roller serving as a pre-cleaning member, to which a positive voltage is applied, and a pre-collection roller serving as a pre-collection member that collects toner attached to the pre-cleaning brush roller. The pre-cleaning brush roller contacts the intermediate transfer belt at a position opposite a conductive pre-opposing roller, around which the intermediate transfer belt is wound. The pre-opposing roller is grounded, and a potential difference used for electrostatically cleaning the toner is formed between the intermediate transfer belt and the pre-cleaning brush rollers by the voltage applied to the pre-cleaning brush roller.
When the untransferred toner image mostly formed of the normally-charged toner, that is, the negatively-charged toner, is conveyed to the cleaning device, much of the negatively-charged toner is electrostatically moved to the pre-cleaning brush roller and removed from the intermediate transfer belt. Accordingly, an amount of toner conveyed to the first and second cleaning brush rollers or the polarity control member, each provided downstream from the pre-cleaning brush roller, is reduced. As a result, the toner still remaining on the intermediate transfer belt after passing through the pre-cleaning brush roller can be reliably removed by the configuration of the first or second example of the related-art cleaning device provided downstream from the pre-cleaning brush roller.
In a case in which the improved configuration is employed in the first example of the related-art cleaning device described above, any reattached toner is removed from the intermediate transfer belt by the second cleaning brush roller. However, the larger amount of reattached toner cannot be sufficiently removed from the intermediate transfer belt by the second cleaning brush roller alone.
By contrast, in a case in which the improved configuration is employed in the second example of the related-art cleaning device described above, the polarity of the reattached toner is reversed to the normal charging polarity, that is, the negative polarity, by the polarity control member so as to be removed from the intermediate transfer belt by the cleaning brush roller. However, in this case also, the larger amount of negatively-charged reattached toner cannot be sufficiently removed from the intermediate transfer belt by the cleaning brush roller alone.